- #1

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##

\frac{d}{d\epsilon}\left(\sqrt{1 + (y' + \epsilon g')^2}\right)

##

where ##y, g## are functions of ##x##

I know I should substitute say ##u = 1 + (y' + \epsilon g')^2##

then use the chain rule, ## \frac{\partial\sqrt{u}}{\partial x} \frac{\partial x}{\partial \epsilon}##

But now I'm a little stuck. Can anyone help with a pointer?

I know what the final answer is, but can't get there.

Thanks